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MATH 1150 · Radical expressions · Objective 1.1

Cube-Root Parent Function

Build y = ∛x from perfect cubes and distinguish it from y = √x.

CLO 1 · Topic 12 of 21
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Build the concept from the beginning

Meaning before procedure

The parent cube-root function f(x) = ∛x accepts every real input, passes through the origin, and is increasing from left to right. Negative inputs produce negative outputs.

Perfect cube
An x-value such as −8, −1, 0, 1, or 8.
Inflection center
The central point (0,0) where the curve changes concavity.
Domain
All real numbers.
Range
All real numbers.

Interactive visual model

Compare the two-sided cube-root parent with the one-sided square-root parent.

Change one control at a time and describe what changes—and what stays invariant.

A dependable four-step method

Choose positive and negative perfect cubes.
Compute cube roots.
Plot symmetric anchor points around the origin.
Connect with an increasing S-shaped curve.
  1. Choose positive and negative perfect cubes.
  2. Compute cube roots.
  3. Plot symmetric anchor points around the origin.
  4. Connect with an increasing S-shaped curve.
Three fully explained examples

Watch the reasoning, not just the answer

Example 1: Find five anchor points on y = ∛x.

Name the goalUse perfect cubes.
Choose the next moveChoose x = −8, −1, 0, 1, 8.
Carry out the mathematicsPoints: (−8,−2),(−1,−1),(0,0),(1,1),(8,2).
Check and interpretCubing each y-coordinate returns x.

Example 2: Decide whether (−27,−3) is on y = ∛x.

Name the goalSubstitute x = −27.
Choose the next moveEvaluate the odd root.
Carry out the mathematics∛(−27) = −3, so yes.
Check and interpret(−3)³ = −27.

Example 3: Compare domains of √x and ∛x.

Name the goalUse index parity.
Choose the next moveEven roots restrict negative radicands; odd roots do not.
Carry out the mathematics√x has domain x ≥ 0; ∛x has all real x.
Check and interpretTheir graphs show an endpoint versus continuation through the origin.
Interactive practice

Predict, decide, check, and revise

Interactive construction lab

Build a valid reasoning path

Choose the decisions in the order a careful solver would use them for this concept.

Choose this step, then check the construction.
Choose this step, then check the construction.
Choose this step, then check the construction.

The reasoning path changes as each decision is selected.

Readiness check

Check the foundation

On y = ∛x, what y-value corresponds to x = -343?

On y = ∛x, what y-value corresponds to x = -216?

Not completed yet.
Guided practice

Apply the method with support

On y = ∛x, what y-value corresponds to x = -125?

On y = ∛x, what y-value corresponds to x = -64?

On y = ∛x, what y-value corresponds to x = -27?

Not completed yet.
Independent practice

Work without step prompts

On y = ∛x, what y-value corresponds to x = -8?

On y = ∛x, what y-value corresponds to x = -1?

On y = ∛x, what y-value corresponds to x = 0?

On y = ∛x, what y-value corresponds to x = 1?

Not completed yet.
Mastery check

Demonstrate durable understanding

On y = ∛x, what y-value corresponds to x = 8?

On y = ∛x, what y-value corresponds to x = 27?

On y = ∛x, what y-value corresponds to x = 64?

On y = ∛x, what y-value corresponds to x = 125?

On y = ∛x, what y-value corresponds to x = 216?

Not completed yet.
Unfamiliar transfer

Explain, compare, and revise

Explain why the cube-root graph includes Quadrant III while the square-root graph does not.

Write a first attempt before opening the self-check.

The learner record reveals exact answers and model reasoning only after an attempt.